Most fishermen make a connection between weeds and fish. As well they should. North American Fisherman has been preaching the gospel of probing weedlines, inside turns and weed-fringed pockets for years. But few anglers fully understand the relationships between aquatic vegetation, fish behavior and the very health of our beloved fisheries.
Ray Valley does. A devout bass fan, he figures weedgrowth into many of his fishing strategies. But the roots of Valley’s interest in vegetation run deeper than that. In college, he wrote his master’s thesis on milfoil’s effect
on largemouth bass feeding success. Today, he’s a nationally respected research biologist with the Minnesota Department of Natural Resources—and his studies are at the forefront of efforts to explore, better understand and protect aquatic vegetation.
Using highly advanced sonar, GPS mapping units and computer software, Valley surveys this mysterious frontier, and the colorful maps he produces are the envy of anyone who fishes weeds. Valley also studies vegetation’s relationship to fish.
Besides pondering the link to bass, he pays special attention to high-risk native minnows such as blackchin shiners and banded killifish, as well as Iowa darters, diminutive relatives of walleyes and saugers. Because these small fish share the same habitat as juvenile bass and many other gamefish, any signs of habitat loss should send up red flags to the angling community.
How It’s Done
Let’s start with the maps. Valley’s research boat is armed with an amazing sonar array even the spendiest tournament rigs can’t match.
“I use a Biosonics DE-6000 digital echosounder with a 430 kHz, 6-degree, split-beam transducer,” he explains. “The setup runs around $32,000 so it’s a little steep for most anglers. But you need it to get an accurate picture of what we call ‘biovolume,’ which is basically the amount of water column filled with vegetation.”
Using a ping speed of five pulses per second, Valley slowly motors back and forth across a lake in transects roughly 30 feet apart. A high-end GPS plotter blends course coordinates with sonar information and offers reports every two seconds.
After the initial sonar run, Valley plugs the resulting data into Biosonics EcoSAV software. In a move approaching rocket science, the program’s advanced algorithm calculates the depth, height and thickness of vegetation based on the sonar returns. In short order, Valley has a detailed, accurate picture of what lies beneath the surface. Maps resemble common contour charts, with an overlay of information on weedgrowth.
“It offers a perspective on underwater landscapes similar to what aerial photography and satellite imagery have provided of ecosystems on dry land for years,” he explains.
Resource managers and anglers alike can use vegetation maps from Valley and other sources (see sidebar). Biologists can assess the health of a lake’s weedbeds, and track changes by season—as well as longterm declines. They can also gauge water quality and identify critical areas to protect from development and other threats. In lakes infested with exotic vegetation, they can also monitor an invader’s spread, and target control efforts to appropriate areas.
Anglers, on the other hand, can use the maps to pinpoint prime fishing areas long before they get to the lake, and avoid wasting valuable time on the water searching for fish. Imagine being able to plot a milk run of weedlines, points, pockets and inside turns from the comfort of your home office, then running from one to another once you’re on the lake.
While much of Valley’s research has focused on vegetation, he recently added fish to the mix. Right now he’s finishing up a three-year study of fish location relating to weedgrowth, and his findings are of interest to fishermen for several reasons.
From a selfish standpoint, we can all appreciate what he learned about adult fish location. While juvenile gamefish and minnows stick to shallow near-shore water, mature bass, pike and other predators tend to favor what Valley calls the “offshore zone” of vegetation, lying in six to 12 feet (depending on water clarity). “They’re creatures of the edge,” he explains. “The more edge you have, the more fish a lake can produce.”
You’re probably nodding your head and thinking, “I knew weedlines held fish.” But don’t stop there. Think about Valley’s last sentence. If research shows us that edge equals fish, and you’re choosing between two lakes for a Saturday outing, do you think it’s a smart idea to consider which one has the most weedlines?
One more important point on weedlines: Predators cruise the edge, or lurk just inside the weed canopy, waiting for prey to pass within striking distance. So it makes sense that edges are prime fishing areas.
But don’t limit yourself to just the inside and outside edges of a bed. For example, Valley points out that when weed-control programs cut lanes within a weedbed, like spokes inside a wheel, the inner lanes attract cruising predators and become prime lies for anglers.
Such spokes won’t show up on run-of-the-mill contour maps. You may luck out and find an aerial map that shows them, but most of the time you’ll have to locate them with sonar; by looking for visual clues like an absence of weedtops within a bed; or by fishing your way through the weedgrowth. Anglers willing to put in the extra effort can have some great fish-holding weedlines all to themselves.
One way to simplify the process is to contact lake associations or the agencies responsible for weed control and find out when and where cutting has taken place. On lakes where chemical control or widespread cutting has occurred, focus on finding patches of weeds that survived the onslaught. Such beds can be loaded with “refugees” from weeds destroyed by control efforts.
Another point to consider when deciding which lake to fish is the amount of vegetation it has along shore. No, you probably won’t find many gamefish in thick weeds in a foot or two of water. But remember that young gamefish love them.
“The more near-shore weedgrowth, the better it is for juvenile bass, walleyes and other gamefish,” Valley says. The more young bass, crappies and pike that reach adulthood, the better the fishing will be.
When it comes to targeting weedbeds by plant species, Valley says, “From a fish’s standpoint, native vegetation is best, but non-native plants are better than nothing.” In other words, cabbage, coontail and bulrushes are ideal, but a milfoil bed beats a barren bottom.
So why do anglers often catch so many bass from stands of exotic milfoil? Valley has some thoughts on the subject.
“When I did my thesis work on largemouth predation on bluegills in milfoil, I found that the bass had a hard time feeding amid the milfoil stalks beneath a really dense canopy,” he says. “So when I hear about anglers catching bass around milfoil beds, I wonder whether the lake is producing more bass because of the milfoil, or whether the fish just got forced to the edge of the beds, where they are more vulnerable to fishing pressure.”
In the end, Valley’s research produced fish-location maps that are virtually a mirror image of the vegetation charts. Where there are healthy weedbeds, there are fish. Which is why, as a biologist and an angler, he’s far more concerned with the future of aquatic vegetation than he is about simply finding a hot weedbed for his next day of fishing.